Sinkhole answers elusive

Thursday

Jan 31, 2013 at 11:09 AM

It will take more than two months for scientists to get a better idea of the dangers a sinkhole poses for the Bayou Corne community.

Xerxes WilsonStaff Writer

It will take more than two months for scientists to get a better idea of the dangers a sinkhole poses for the Bayou Corne community.About 100 residents gathered Wednesday night at the Assumption Parish Community Center to hear spokesmen and contractors from Texas Brine explain their efforts to contain and better understand dangers presented by the massive hole.The sinkhole appeared Aug. 3 swallowing acres of swampland and trees and prompting an evacuation order for about 150 homes nearby.The hole has grown to encompass about 8.6 acres, with another seven or so acres around it sinking. It is more than 200 feet deep, which is shallower than before as its sides continue to cave in and settle.Scientists have said they believe the hole was caused after a subterranean cavern collapsed displacing the ground above. The cavern was situated inside the Napoleonville Salt Dome, an underground solid salt formation. Texas Brine used the cavern to produce brine, a salty substance used in construction and oil-drilling operations.Because of the logistical challenges of taking images thousands of feet underground, scientists do not know with certainty the condition of the ground under the sinkhole or if other voids exist under the surface that could cause the hole to grow or another hole to form.The hole has also sent naturally occurring petroleum and gas toward the surface, with natural gas accumulating in the area's aquifer. This creates the potential for the gas to dangerously accumulate in enclosed spaces above the surface.Because of this, the evacuation order issued in August will remain in place, said John Boudreaux, Assumption Parish Emergency Operations director.Much of Wednesday's meeting was devoted to discussion of how Texas Brine is going to figure out how stable ground below Bayou Corne is and where and how much natural gas lingers under the ground.Their plan, as explained by geophysicist Kevin Hill, is to create a three-dimensional image of the ground below the area over the next two months. The image of the western edge of the Napoleonville Salt Dome going down 7,000 feet will be used to identify underground pockets where gas needs to be bled off as well as the possibility of any voids still lurking in the ground below.“It's a little tricky, but after having done this for 35 years, this is going to be the fastest and safest way to get a really fine snapshot of the subsurface, what is under your feet,” said Hill, who has been contracted by Texas Brine to design the imaging process.That process came under heavy scrutiny from frustrated residents, some of whom have been out of their homes for six months and never plan to return.“If something happens, I want to know who is buying it and for how much,” said Bayou Corne resident Nick Romero about his home of 20 years.Hill will be using a process called active seismic imaging, which employs a series of “thumps” and sensors to create an image of what's underground.The “thumps” consist of airguns, various vibrating devices and firecracker-sized explosives placed underground. These devices, more than 2,500 of them, send waves into the ground. These waves travel faster through various types of ground and liquid. Eventually, the waves will be read by a network of more than 2,600 sensors placed into the ground in the area. This information will allow scientists to create the three-dimensional image of the ground below, but residents must agree to allow the “thumps” and sensors to be placed on their property.Residents were concerned the “thumps” would cause damage to their home. “We want to find out what is going to happen to our homes, so you have to understand our skepticism,” said Ken Simoneaux, who has been out of his home for six months.Hill insisted the vibrations would be no greater than a truck passing by. Contractors have also been hired to monitor the process and ensure any damage caused is repaired.“What choice do we have,” asked resident Mike Daige. “I don't feel like there is any other solution; we have to see what is down there.” Daige signed the agreement allowing contractors to access his land, which he says he never plans to live on again. “As soon as I can find a buyer, I'm done with it,” Daige said. “I was gone right after the hole first appeared.” Hill said if all goes well, the images should be available by April 15.The parish is planning another meeting for Wednesday at the Community Center, where state officials will discuss their plans for the hole.